Alexander McQueen creative director Sarah Burton told a small group of big-spending shoppers at Saks Fifth Avenue yesterday that Kate Middleton “couldn’t have been more lovely” as they worked together on her stunning dress for her wedding to Prince William. Burton, speaking to customers including Meredith Vieira and Grace Hightower at an event for personal shoppers, told one guest the dress “was a collaboration” between her fashion house and the new Duchess of Cambridge, adding, “It was made for her and has a lot of her personality in it.” She said Kate’s family — including her sister, Pippa, whom Burton also dressed as maid of honor — were “really nice and down to earth.” But Burton poked fun at the massive guessing game over the dress design and how she had to hide under a huge fur hat to avoid photographers at Kate’s hotel, The Goring, for a fitting the day before the wedding. She said, “The most fun I had was trying to hide . . . we laughed a lot about that.”